1. Field of the Invention
The present invention relates to a method of manufacturing a gallium nitride based light emitting diode (hereinafter, referred to as a GaN-based LED), which can simplify the overall manufacturing process of a GaN-based LED having a transparent electrode and a protective film.
2. Description of the Related Art
In general, a nitride semiconductor is such a material that has a relatively high energy band gap (in the case of GaN semiconductor, about 3.4 eV), and is positively adopted in an optical element for generating green or blue short-wavelength light. As such a nitride semiconductor, a material having a compositional formula of AlxInyGa(1-x-y)N (herein, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1) is widely used.
Since GaN-based semiconductor crystal can be grown on an insulating substrate such as a sapphire substrate, electrodes cannot be formed on the rear surface of the substrate as in a GaAs-based LED. Therefore, both electrodes should be formed in the side of a crystal-grown semiconductor layer.
For this, a process of forming a mesa structure is required. In the mesa-structure, some regions of an upper clad layer and an active layer are removed so that a portion of the top surface of a lower clad layer is exposed.
Since a p-type GaN layer formed of the upper clad layer has relatively high resistance, an additional layer is required in which ohmic contacts can be formed by using a typical electrode. Accordingly, before an electrode is formed on a p-type GaN layer in the related art, an Ni/Au transparent electrode is formed so as to form ohmic contacts, thereby reducing a forward voltage Vf. As for the transparent electrode, an ITO (indium titanium oxide) film may be used.
As such, the mesa structure formation process, the transparent electrode formation process, and the bonding electrode formation process are needed in order to manufacture a GaN-based LED according to the related art. Additionally, a protective film formation process is separately accompanied in manufacturing a GaN-based LED. Therefore, the overall manufacturing process becomes complex. Such complexness can be found in a process example shown in FIGS. 1A to 1G
FIGS. 1A to 1G are sectional views sequentially showing a process for explaining a method of manufacturing a GaN-based LED according to the related art.
As shown in FIG. 1A, the process begins with a primary growth process in which an n-type GaN layer 111, an active layer 113, and a p-type GaN layer 115 are sequentially formed on a transparent insulating substrate 100 formed of sapphire. At this time, the n-type GaN layer 111, the active layer 113, and the p-type GaN layer 115 can be formed by such a well-known nitride growth process as MOCVD.
Next, as shown in FIG. 1B, a process of forming a mesa structure is performed in order to form an n-electrode (not shown) on the top surface of the n-type GaN layer 111. More specifically, the mesa structure formation process includes forming first photoresist PR1 on the top surface of the p-type GaN layer 115 excluding a region to be etched; and etching and removing predetermined regions of the p-type GaN layer 115 and the active layer 113 by using the first photoresist PR1 as an etching mask such that a portion of the top surface of the n-type GaN layer 111 is exposed.
Subsequently, after the first photoresist PR1 for forming the mesa structure is removed, a transparent electrode 120 is formed on a predetermined region of the p-type GaN layer 115 exposed by removing the first photoresist PR1, as shown in FIG. 1C.
After that, as shown in FIG. 1D, a p-electrode 140 and an n-electrode 130 are formed on the transparent electrode 120 and the exposed n-type GaN layer 111, respectively, through a typical electrode formation process.
Then, as shown in FIG. 1E, a protective film 150 formed of such a material as SiO2 or SiN is formed on the entire top surface of the resulting structure where the p-electrode 140 and the n-electrode 130 are formed.
Subsequently, as shown in FIG. 1F, second photoresist PR2 is formed on the top surface 150 such that portions of the protective film 150 corresponding to the p-electrode 140 and the n-electrode 130 are exposed.
Next, as shown in FIG. 1G, the protective film 150 is selectively etched and removed with the second photoresist PR2 set to an etching mask. Accordingly, the p-electrode 104 and the n-electrode 130 are exposed.
As described above, in the method of manufacturing a GaN-based LED according to the related art, the overall manufacturing process is complex. Further, since a SiO2 or SiN film used as the protective film has poor adhesion performance with the electrodes, that is, the transparent electrode 120, the p-electrode 140, and the n-electrode 130, defective adhesion (for example, the film can be peeled off) occurs, thereby reducing characteristics and reliability of the diode.